SWATH stands for ‘Small Waterplane Area Twin Hull’, an innovative concept for smooth service in rough seas. The buoyancy of a SWATH ship is provided by two submarine hulls connected to the upper platform by twin narrow struts from each of the submarine hulls, as shown in the image below. The cross-sectional area at the sea surface is approximately 1/6th that of a comparable size yacht and thus only a minimum part of the ship is exposed to the lifting forces of the waves while 5/6 of the buoyancy is on the submarine hulls. Additional stability is provided by the SWATH’s broad beam which is twice that of a comparable yacht and by four large stabilizers controlled by a sophisticated computer system. The idea of SWATH was taken from the principle of semi-submersible offshore rigs, which are designed to provide a working platform with minimized motions in open seas. As scuba divers and submariners will attest, one needs to be only slightly under the surface of the sea to be in a calm environment regardless of conditions on the sea surface.

Silver Cloud article from April 2009 issue of Boat International (European Edition)